The present invention relates to controlled wheel braking systems and more particularly to a controlled wheel braking system which is resonsive to wheel lock up. The controlled wheel braking system of the present invention has particular utility in automotive vehicles, trucks, airplanes, tractors and the like.
The greatest deceleration of a vehicle occurs immediately prior to wheel lock up. As the operator of the vehicle increases the fluid pressure in the braking system, and, thus, the force of the brake shoes on the brake drum, vehicle deceleration is increased. When the fluid pressure in the braking system is increased beyond a certain optimum, the vehicle starts to skid thereby decreasing the actual rate of deceleration of the vehicle.
Naturally, it is highly desirable to employ a braking system which allows for optimum deceleration of the vehicle while at the same time prohibits the vehicle from skidding. By providing a system where fluid pressure is decreased at the instant of wheel lock up, the danger of skidding is eliminated and optimum vehicle braking is obtained.
U.S. Pat. No. 4,265,343 discloses an entirely mechanical controlled wheel braking system which is responsive to wheel lock up so as to prevent skidding upon initial application. However, if the road surface coefficient of friction should change, due to snow, ice patches, water, etc. during the application of the brake the operator would be required to release and reapply the brake to compensate. If the road surface coefficient of friction varies significantly the release and reapplication, i.e., pumping of the brake may have to be done a number of times during a single stop thus requiring significant skill by the operator in order to maintain optimum braking without skidding.
In order to overcome the foregoing, it would be highly desirable to design a controlled wheel braking system wherein fluid pressure is relieved upon sensing wheel lock up and the brakes are automatically pumped so as to maintain optimum braking of the vehicle while preventing skidding.
Accordingly, it is the principal object of the present invention to provide a controlled wheel braking system in which the wheels of a vehicle are prevented from skidding regardless of changing road conditions and the fluid pressure applied by the operator.
It is a particular object of the present invention to provide a controlled wheel braking system in which the brakes are automatically pumped so as to optimize the braking of a vehicle regardless of changing road conditions.
It is a still further object of the present invention to provide a controlled wheel braking system which is of simple construction, inexpensive to manufacture and dependable in service.
Further objects and advantages of the present invention will be apparent from a consideration of the ensuing disclosure.